Tree Seed Workshop 2007 Dave Kolotelo

Transcription

1 Tree Seed Biology Tree Seed Workshop 2007 Dave Kolotelo

2 Dave s s Top 7 Take Home Messages 1) Collection timing, method and subsequent handling of cones (interim storage) can have a large impact on seed quality. 2) Cone and seed processing activities are aimed at optimizing tradeoffs between seed quality and quantity (yield). They can also greatly impact seed quality. 3) Conifers possess orthodox seeds which can be stored at low moisture contents at subfreezing temperatures. Good Storability.

3 4) Seed needs to be imbibed (hydrated) before dormancy removal or germination will occur. 5) Most conifers possess some type of dormancy mechanism that needs to be overcome before germination will occur. 6) Cold stratification is probably the closest we get to a panaceae in Forestry 7) Cone and seed handling practices have improved greatly, but we are often left with the legacy of our ignorance. Panaceae = a remedy for all ills or difficulties

4 Basic Concepts Seed is a living biological end-product of genetic and environmental interaction and its behaviour cannot be predicted with certainty Forest tree seeds (+shrubs, ground vegetation) are in a relatively wild state compared to agricultural crops genetic diversity complicates direct adoption of agricultural seed hanling techniquesand methods

5 Gymnosperms million years old 70 genera species naked seeds - not contained in ovules storage reserves from female parent (1n) Angiosperms million years old about species an ovary covers the seed storage reserves from both (3n) dicots and monocots

6 Morphology The study of external form and structure of organisms seed size seed shape presence of structures (wing, resin vesicles) seed condition (moisture level, health)

7 Within-Seedlot Variability Py Sx

8 Pli vs. Sx Morphology Pli generally darker, larger (size & weight) and with ridges on the seed coat there will be an overlap at the extremes of both species Seeds are similar, but time from pollination drastically different (1 year later in Pli) Pli Sx

9 Py Pli Lw Fd_ Pw Yc

10 Wet vs.. Dry Pli Fd?

11 Resin Vesicles Present in Hw, Hm, Cw and all Abies spp. Hw Hm Cw Bl Function not known?? protection against excessiove drying may inhibit germination (dormancy) Damaged Ba resin vesicles Damage to resin vesicles will reduce germination

12 Surface moist vs. dry seed Sx

13 Practical Morphology Seedcoat cracking germination mechanical damage Resin vesicle damage Broken vesicles, resin, odour Mycelium indication of fungi, possibly a disease Insect damage - unlikely

14 A vs. B Differences Seed Size orchard-produced seed larger in Pinaceae fairly low heritability (E > G) larger seeds increase sowing efficiency no strong relationship between seed and seedling size - variable results? gains from sowing sized seed fractions not obvious/practical at current request sizes family sowing?? advocated by some, but request sizes still an issue? Related more to seedling growth (recoverables) vs. sowing efficiency

15 Temporal Variation (yr -to- yr) 70 0 Seeds per Gram % smaller seeds Sx You buy seed by weight don t you?

16 A vs. B Differences Germination parameters fairly high heritability (G >E) no large differences between A and B seed except Yc (Environment) - pollen effects? Dormancy can be influenced by environment year-to-year variability no heritability estimates available Method of quantifying dormancy coming!!

17 Anatomy The study of the structure of internal parts of an organism by dissection and magnification cutting tests x-rays prepared slides

18 Seed Anatomy

19 Moisture Uptake Comparison

20 Non-Viable seeds Seeds can be classified based on anatomy, but it is not always possible to determine what happened to the seed

21 classification isn t always black and white

22 Micropylar plug in Pw

23 Sx

24 Pw

25 Yellow cedar

26 Physiology the study of the functions and functioning of organisms and their parts respiration moisture uptake dormancy germination

27 Respiration in Douglas-fir (Leadem 1993) Radicle emergence Dry 1 hr 24 hr 72 hr 6 days <1 mm 1-4 mm 5-10 mm > 10 mm

28 What does a seed need to germinate? Moisture Overcome Dormancy Temperature Sums properly stratified conifer seed does not have a light requirement some angiosperms have more specific requirements - light, alternating temperature and/or moisture,gases, nutrients, smoke Conifers are relatively simple to germinate Efficiency is the isssue large energy input!

29 Moisture Storage at % (minimize metabolism) Seed needs a minimum of about 20% to overcome dormancy 30% appears optimal for most species and this generally is surface-dry seed following adequate imbibition (see Operational Table ) We want to maximize internal moisture without having moisture on the seed coat A Tricky Balance

30 Three Phases of Water Uptake Imbibition -(Reactivation) rapid exponential mc gain initiate cellular metabolism build up of energy for future activities Mobilization -(Breakdown) mc remains stable complex molecules are broken down dormancy is overcome in this phase Emergence -(Buildup) exponential increase in mc buildup of complex molecules - seedling structure

31 Moisture Uptake Comparison

32 Seed Dormancy failure of an intact viable seed to complete germination under favourable conditions in conifers we are usually dealing with physiological dormancy that is overcome by stratification (moist-chilling) cold stratification alters the hormonal balance [ABA +] within the seed to allow germination to proceed in some conifers the outer tissues (seed coat, membranes) can also be involved

33 Dormancy may be perceived as a strategy for optimizing the distribution of germination through space and time in order to maximize survival, but this seldom coincides with the nursery workers objectives

34 Seed Dormancy Physiological or embryo dormancy No Dormancy - Cw Low Dormancy - Hw, Sx, SS, Lw, Fd Mid Dormancy - Pli, Hm, Bg, Py Deep Dormancy -Yc, Pw, Ba, Bl Physical seed coat or membrane dormancy is associated with Pw, Yc, and Py Lots of Variability within a species

35 Stratification Originally used to describe the layering of seeds between moistened material (i.e. cloth, peat, sand, paper) current procedures called naked stratification as no media is used moistened seed placed into polyethylene bags 4 mil (.1 mm) polyethylene allows some oxygen and other gas exchange top should be open to maximize gaseous exchange (availability of oxygen)

36 Stratification Benefits Overcome embryo dormancy to allow germination to proceed Increased speed and uniformity of germination Increased vigour (i.e. increased ability to germinate over sub-optimal conditions) Decreased window of opportunity for pests Activation of natural cellular repair mechanisms

37 Optimum Moisture Content in Pli 86 Germination Capacity (%) % 25% 30% 35% 45% Stratification Moisture Content

38 Stratification Moisture Content Variability 5-year average ( ) BA BG BL FDC FDI-A FDI-B HM HW-A HW-B LW-A LW-B PLC PLI PW PY SB SS-A SS-B SX-A SX-B SXS YC Stratification Moisture Content (%)

39 Stratification increases Vigour G erm ination Cap acity (% ) Germination Temperature ( C) 0 wks 3 wks

40 Family Variability W1 G20 Pli Clone #

41 A- class Fdc - 0, 3, 8 weeks Stratification US BC seedlots from each origin used

42 Dry-back and Strat.-Redry In 1986 three research papers were published illustrating the benefits of split stratification Edwards, D.G.W Special prechilling techniques for tree seeds. J. Seed Tech. 10: Leadem, C.L Stratification of Abies amabilis seeds. Can. J. For. Res. 4: Tanaka, Y and D.G. W. Edwards an improved and more versatile method for prechiling Abies procera Rehd. seeds. Seed Sci. Technology 14:

43 G44 vs. G64 G44 45% 35% G

44 Abies moisture content stratification -redry or dryback requires moisture content control former procedures utilize visible clues and timings to obtain proper moisture content 45%++ - drain excess moisture 30-35% - dryback currently we use target moisture content calculations (use of seed weight to estimate seed moisture content)

45 Western White Pine Complex dormancy in Pw None Seed coat Membrane Physiological 1996 new test type for Pw (G55) 20% gain in germination Lab gains not duplicated in operations??? Lots of trial work Now Target stratification m.c. to 37% (34-40% OK) Recommend 3-week stratification extension Limit bag size to 750 g (other sp g) Use larger bag (improve aeration) Monitor and mix each unit M, W, F QA on all Pw seedlots Pw Dormancy from Hoff (1987)

46 Temperature If adequate moisture is available and dormancy is overcome then temperature is the rate limiting factor biological limits exist (30-35 C) that depends on moisture content and species increased germination temperatures result in faster, more uniform germination that also reduces window of opportunity for pests soil or grit temperature more useful more in the Germination Environment talk

47 Seed Deterioration 1) Seed will first lose vigour (ability to germinate under sub-optimal conditions) 2) then loose ability to germinate normally 3) then die (no germination) Theories depletion of food reserves alteration of chemical composition membrane alteration enzyme alteration genetic damage

48 Seed Deterioration Δ Germination% per year Pli Sx Fd Lw Hw Cw minimize metabolic activity (mc, temp) quantified as Δ GC / year large variation between species used to specify species retest frequencies variation also exists within species

49 Additional Seed Biology Information Seed Handling Guidebook Kolotelo, Van steenis, Peterson, Bennet, Trotter and Dennis Tree Seed Working Group Newsbulletin - free electronic newsletter New Tree Seed Centre web page Tic Talk - Tree Improvement + Newsletter - periodically Journals Seed Science and Technology Seed Science Research Seed Technology Canadian Journal of Botany Canadian Journal of Forest Research Tree Planters Notes Forest Nursery Notes Books Bewley and Black,Seeds - Physiology of Development and Germination Farmer, Seed Ecophysiology of Temperate and Boreal Zone Forest Trees

50 Dave Kolotelo Cone and Seed Improvement Officer BCMOFR Tree Seed Centre Tree Improvement Branch (604) ext